Preheat the oven to 180°C (360°F).
Mix bananas, maple syrup, coconut oil, almond milk and apple vinegar in a bowl until the ingredients are well mixed.
Sift the flour, chlorella, baking powder and baking soda into another bowl; then add the oat flakes, salt, cinnamon and nuts.
Mix the wet mixture with the dry ingredients.
Line a cake tin with baking paper, pour in the mixture and distribute evenly.
Cut the banana lengthwise into two halves and place them on the mixture.
Bake in the middle of the oven for the first 30 minutes and at 150°C (300°F) for the remaining 20 minutes.
Remove the cake from the oven and sprinkle with the chocolate pieces.
Let it cool completely before serving.
Enjoy your cake!